System and method for operating a boiling water reactor-steam turbine plant

ABSTRACT

A turbine follow control system for a boiling water reactorsteam turbine plant includes an electrical reference system which determines the reactor operating level through a reactor control system. The turbine follow control system operates turbine steam valves and steam bypass valves electrohydraulically to control the stem throttle pressure as the level of reactor operation is controllably varied to produce required steam flow. In another arrangement, a coordinated control system for a boiling water reactor-steam turbine plant includes an electrical reference system which simultaneously determines the reactor operating level and the turbine steam flow subject to throttle pressure control constraints.

nited States Patent [72] Inventor Lemma 1; p d l k 3,061,533 10/1962Shannon et al. 176/56 wil i mn, D L 3,097,489 7/1963 Eggenberger et al.60/73 [21] PP 779,075 Primary Examiner-Reuben Epstein [22] Flled 1968Attorneys-F. l-l. Henson, R. G. Brodahl and E. F. Possessky [45]Patented Dec. 28, 1971 [73] Assignee Westinghouse Electric CorporationPittsburgh, Pa. ABSTRACT: A turbine follow control system for a boilingwater reactor-steam turbine plant includes an electrical referencesystem which determines the reactor operating level {54] SYSTEM ANDMETHOD FOR OPERATING A through a reactor control system. The turbinefollow control BOEING WATER REACTOR'STEAM TURBINE system operatesturbine steam valves and steam bypass valves PLANT electrohydraulicallyto control the stem throttle pressure as 11 Claims 3 Drawing Figs thelevel of reactor operation is controllably varied to produce [52]U.S.Cl. 176/24, required steam another arrangement, a Coordinated 17 207 55 0 73 control system for a boiling water reactor-steam turbine plant[51] Int. Cl. G2lc 7/36 includes an electrical reference system whichSimullaneously 50 Field of Search 176/20, 24, determines the reactorOperating level and the turbine Steam 25 5 5 56; 50 73 flow subject tothrottle pressure control constraints.

[5 6] References Cited UNITED STATES PATENTS 3,042,600 7/1962 Brooks176/20 THROTTLE IM PULSE PRESSURE PRESSURE DETECTOR DETECTOR INLET STEAMVALVES STEAM LR TURBINE GENERATOR J 38 SECTION 1 were i 2 REACTOR 36 l42 PUMPS 2a VALVES BYPASS SPEED VALVES DETECTOR l 32 TSTEAM v 1 l (30HYDRAULIC HYDRAULIC BYPASS IN LET CONDENSER VALVE VALVE STEAM ACTUATORSACTUATORS SEPARATORS cogggox. 52 1 54 T [F AND (34 ELECTRO- ELECTRO- lREHEATERS DR'VES HYDRAULIC HYDRAULIC ND DEMNERAL'ZER BYPASS VALVE INLETVALVE FEEDWATER CONTROLS CONTROLS HEATER 48 25$8E FEEDWATER FEEDWATER TOREACTOR SYSTEM FROM REACTOR sv E SYSTEM B DETECTORS 81' M ROLLED SYSTEMAND METHOD FOR OPERATING A BOILING WATER REACTOR-STEAM TURBINE PLANTCROSS-REFERENCE TO RELATED APPLICATIONS Ser. No. 779,091 entitledimproved Method and Feedforward System for Operating a Boiling WaterReactor-Steam Turbine Plant filed by T. C. Giras and L. B. Podolsky onNov. 26, 1968 and assigned to the present assignee.

BACKGROUND OF THE INVENTION The present invention relates to steamturbine plants and more particularly to electric powerplants operated bysteam turbines for which the steam supply is provided by a nuclearboiling water reactor.

In a boiling water nuclear reactor, the nuclear fuel is structured witha suitable geometry to provide for a sustained chain nuclear reaction asthe coolant water passes through the fuel arrangement. Conventionally,the nuclear fuel is housed in elongated metallic tubes which are in turnassembled and supported in parallel arrays or bundles. The reactor coreis formed from an assembly of the fuel bundles and it is housed in alarge pressure vessel with provision for coolant flow along all of thefuel elements. Neutron absorbing control rods are supported within thecore for movement relative to the fuel elements.

The design of the core and other reactor parameters determine thereactor power rating. Mechanical, nuclear, hydraulic and other detailsof the reactor design are the result of development programs aimed atachieving efficient performance for the plant owner.

Since water density is a large determinant of the rate of generation ofslow neutrons which are required for the controlled propagation of thechain nuclear reaction, the power operating level of the reactor ispartly determined by the accumulation of steam voids in the core volume.increased coolant flow causes faster fuel rod cooling with reducedboiling and accordingly reduced void accumulation and higher reactorpower. Decreased coolant flow has the opposite effects. Typically,coolant flow control can be used to control the boiling water reactorpower level within a range of about 20 percent or 25 percent with presetcontrol rod placement.

The reactor generated steam is normally directed through separators anddryers within the pressure vessel, and the dry saturated steam isdirectly channeled at a pressure such as L000 p.s.i. and a temperaturesuch as 545 F. to the utilization equipment, i.e., the turbine generatorunit(s) of the electric powerplant. Separated water is combined in thepressure vessel with external and internal recirculation flows and withreturn and makeup feedwater flow.

Since the boiling water reactor plant is the direct cycle type and sinceoutlet steam pressure and reactor vessel pressure affect the voidaccumulation in the reactor core, it is desirable to operate the turbineinlet valves to determine'the turbine and generator load level subjectto pressure-regulating demands of the reactor. With reactor pressuremaintenance within a relatively narrow pressure band such as about 30p.s.i., reactor power level is controlled by coolant flow control withina limited range or by control rod movement if a different power range isrequired to meet load demand on the turbine generator unit(s).

In general, the steam turbine energization level is determined by theflow of the turbine inlet steam which in turn is determined by the steamconditions at the outlet of the steam source and by steam inlet valvepositioning. The turbine drive power supplied for the plant generator(s)is desirably controlled to satisfy electrical load demand and frequencyparticipation demand placed on the electric powerplant by the plantoperator or by an economic dispatch computer or by other means.

At substantially constant temperature'throttle steam, turbine power isproportional to turbine steam flow, and if the throttle pressure is alsosubstantially constant the steam flow is proportional to the impulsechamber steam pressure or the ratio of the impulse chamber steampressure to the throttle steam pressure. As already indicated,positioning of the inlet steam valving must provide for reactor vesselpressure regulation as well as turbine energization level control. Whenthe boiling water reactor power level corresponds to the plant loaddemand, the turbine inlet valves are positioned to produce both thedesired reactor vessel pressure and the turbine steam flow required forsatisfying plant electrical load demand.

A steam bypass system is also usually provided to direct steam flow fromthe reactor outlet to the plant condenser under certain conditions.Steam bypass in effect provides an interface between the boiling waterreactor and the steam turbine during reactor startup and shutdown andduring other periods such as during load rejection. in these cases,steam supplied by the reactor but not needed by the turbine is channeledto the condenser under control imposed on the bypass system by thethrottle pressure control system.

To control a boiling water reactor-steam turbine plant, it has beencustomary to use the turbine follow mode of operation. After plantstartup, corrective changes are made in the reactor power level byautomatic or manual reactor coolant flow control or by manual orpossibly automatic control rod operation in order to satisfy plant loaddemand. Turbine throttle pressure is sensed and the turbine inlet steamvalves are operated in the follow mode to control the throttle andreactor vessel pressures and enable turbine steam flow changes to bemade to correct the turbine load as the reactor power level is beingcorrected. To speed up the control particularly when step changes aremade in load demand, the setpoint of the turbine pressure control may betemporarily adjusted in response to the load error.

In the typical boiling water reactor-steam turbine application, the partof the control system directed to turbine valve control is principallymechanical and hydraulic in character with some electrical circuitrysuch as that involved in the throttle pressure sensing function.Examples of principally hydraulic turbine inlet valve feedback controlsin nonnuclear applications are set forth in US. Pats. to Bryant, No.2,552,401 and Marsland, No. 1,777,470. A principally mechanical turbineinlet valve feedback control is shown in US Pat. to Eggenberger, No.3,027,137 in a nonnuclear application. Electrohydraulic analogfeedback-type turbine inlet valve controls have been employed innonnuclear turbine applications to achieve operational improvements, andexamples of such controls are presented in US. Pats. to Bryant, No.2,262,560, Herwald, No. 2,5l2,l54, Eggenberger, Nos. 3,097,488;3,097,489; 3,098,176 and Callan, No. 3,097,490.

One shortcoming of the nuclear turbine prior art has been an inabilityto provide backup speed control uniformly without dependence on turbineoperating load level. At a low load level, the turbine might typicallybe subjected to backup speed control-in addition to pressure control atpercent of synchronous speed while at a higher load level the turbinemight be subjected to backup speed control at a lower speed such as lOlpercent of synchronous speed. It is generally desirable for plant safetyand system security reasons to provide a substantially fixed turbinespeed valve at which inlet steam pressure control is supplemented bybackup speed control, and prior art systems have not had this capabilityprincipally because fluid pressure control of the backup speed controlis auctioneered with that of the pressure control and thus the speederror required for implementation of speed control is dependent on theload level.

More generally, although prior art boiling water reactorsteam turbineplant operation has been more or less satisfactory, it has beencharacterized with performance deficiencies including deficiencies insystem response speed and the extent of plant or system coordination. inturn, prior art plant operation has been less secure, less economic andless efiicient than it might otherwise be. Thus, the turbine followcontrol scheme produces time delay in system load-generating performancesince the boiling water reactor control must first change the reactorpower level and incur the reactor response time before the turbinecontrol valves are moved by the pressure control to correct a plant loaddemand error. As reactor power changes toward the demand power level,the reactor vessel and throttle pressure conditions change to allow thepressure control to move the turbine control valves and change theturbine steam flow toward the correct value.

Some reduction in the turbine follow delay and some improvement in plantcoordination has been achieved by anticipatory operation of the throttlepressure control, i.e., the throttle pressure setpoint is adjusted atthe same time that the reactor load level is adjusted to correct a loaddemand error so that the turbine control valves begin moving sooner inresponse to the throttle pressure control setpoint adjustment. In thismanner. energy stored in the reactor steam is used within presetconstraints on throttle pressure to obtain faster system response. Asreactor power changes to correct the load demand error, the pressurecontrol setpoint adjustment is withdrawn. Thus, the throttle pressuresetpoint adjustment technique is anticipatory in the sense that it isemployed to speed up the process response with the expectation thatutilized stored system energy will be replaced by control imposed on theboiling water reactor.

Although throttle pressure setpoint adjustment has some merit from ananticipatory control standpoint as already indicated, it is deficient inthat it still incurs the control system response delay of a conventionalthrottle pressure control. Further, throttle pressure setpointadjustment involves a fixed characterization of the amount of throttlepressure setpoint adjustment to be provided as a function of time andload error. This relative inflexibility in throttle pressure setpointadjustment in the throttle pressure control limits the turbine controlvalve operation to relatively gross anticipatory operation withoutspecific calibration for best or nearly best system response overvarying load demand, throttle pressure and other system conditions.Plant coordination and load response have accordingly been adverselyaffected.

Another general shortcoming of the turbine follow scheme of plantoperation has been the fact that loss of throttle pressure controlrequires detection and some form of control action which either placesthe turbine under manual control or under another form of automaticcontrol. The time lost in making the changeover includes the detectionand initiation time as well as the time required to update the newcontrol loops to present plant conditions. A deficiency thus occurs inplant coordination and it is desirable that it be avoided even if thecontrol action time involved is relatively small.

SUMMARY OF THE INVENTION In accordance with the broad principles of theinvention, a system and method for operating a boiling waterreactorsteam turbine plant involve a reactor control system and turbinevalve and bypass valve electrohydraulic control systems which areoperated to satisfy electrical references for plant load and turbinespeed. In a turbine follow control scheme, the turbine and bypass valvesare operated by a throttle pressure control to satisfy throttle pressureconstraints as load demand is being met with changed reactor powerlevel. A backup speed control electrically supplements the pressurecontrol of the turbine control valves independently of turbine loadlevel when the turbine speed reaches a predetermined value.

In a coordinated control scheme, extended system coordination and fastersystem response is achieved since both the turbine valve control and thereactor control systems are made dependent on the load reference.Pressure control means are provided for limiting the turbine valvecontrol system operation to satisfy throttle pressure constraints aschanges in load demand are met.

The pressure control means preferably is operative in response to afeedback ratio of the turbine impulse chamber steam pressure to thethrottle steam pressure in order to negate positive feedback actionotherwise imposed on the turbine control valves when impulse chambersteam pressure is used alone as the feedback variable. To hold thethrottle pres sure within a predetermined range of allowable values, thepressure control means further preferably is operative in response tothrottle pressure error. The pressure control means also determines theoperation of the bypass valve system in order to divert steam in excessof turbine needs directly to the plant condenser.

The invention is practiced with the electrical portions of the controlsystems embodied as analog control circuitry or digital controlcircuitry or as some combination of analog and digital controlcircuitry. When digital hardware is employed, a programmed digitalprocess computer can be included in the control circuitry.

It is therefore an object of the invention to provide a novel system andmethod for operating a nuclear boiling water reactor-steam turbinepowerplant with improved efficiency and economy.

It is another object of the invention to provide a novel system andmethod for operating a nuclear boiling water reactor-steam turbinepowerplant with improved backup speed control.

A further object of the invention is to provide a novel system andmethod for operating a nuclear boiling water reactor-steam turbinepowerplant with improved coordination.

An additional object of the invention is to provide a novel system andmethod for operating a nuclear boiling water reactor-steam turbine powerplant with faster system response.

These and other objects of the invention will become more apparent uponconsideration of the following detailed description along with theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I shows a schematic diagram of anelectric powerplant operated by boiling water reactor and steam turbineapparatus;

FIG. 2 shows a schematic diagram of a turbine follow control systemarranged in accordance with the principles of the invention to operatethe plant of FIG. 1;

FIG. 3 shows a schematic diagram of a coordinated control systemarranged in accordance with the principles of the invention to operatethe plant of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT More specifically, there isshown in FIG. I an electric powerplant 10 which is provided with aconventional electric generator 12 operated by a nuclear steam turbine14 in accordance with the principles of the invention. A steamgeneratingsystem for the turbine 14 includes a conventional nuclear boiling waterreactor 16.

The nuclear steam turbine 14 is provided with a single-output shaft 18which drives the generator 12 to produce threephase or other phaseelectric power. Typically, the electric generator 12 is connected (notshown) through line breakers to a large electric power network and whenso connected causes the turbogenerator arrangement to operate atsynchronous speed under steady-state conditions. Under transientelectric load change conditions, system frequency may be affected andconforming turbogenerator speed changes would result. At synchronism,power contribution of the generator 12 to the network is normallydetermined by the turbine steam flow and the throttle pressure at whichthat flow is supplied by the boiling water reactor 16.

In this instance, the nuclear steam turbine 14 is of the multistageaxial flow type and includes a high-pressure section 20 and adouble-flow, low-pressure section 22. Each of the turbine sections 20and 22 may include a plurality of expansion stages provided bystationary vanes and an interacting bladed rotor connected to the shaft18. In other applications. nuclear steam turbines operated in accordancewith the present invention can have other forms with more or fewersections tandemly connected to one shaft or compoundly coupled to morethan one shaft. For example, as many as three or more low-pressuresections might be employed, and each section could have a single flowpath or double or other plural flow paths.

Steam is directed to the nuclear turbine 14 through conventional inletsteam valves 24. Typically, the valves 24 would include two or morethrottle valves (not specifically indicated) which admit steam to theturbine steam chest (not indicated) and a plurality of up to four ormore governor control valves (not specifically indicated) which arearranged to supply steam to turbine inlets arcuately spaced about theturbine high-pressure casing.

The conventional nuclear turbine startup method is employed. Thus, theturbine speed is raised from the turning gear speed of about 2 rpm. tothe synchronous speed under throttle or governor valve control. Then thepower system breaker(s) is closed and the governor valves are operatedto meet the load demand. On shutdown, similar but reverse practices canbe employed or conventional coastdown procedure can be used. In the loadcontrol mode, plant electrical load demand is met when the steam flowand throttle pressure conditions cause the turbine energization level tocorrespond to the plant electrical demand.

The total turbine energization is produced by steam flow through thehigh-pressure section and by steam flow through the low-pressure section22. Steam flow between the two turbine sections is directed throughsteam separators and reheaters as indicated by block 26 in order toraise the steam enthalpy level to a more efficient value. Stop valve(s)are included in the steam flow path between the turbine sections to stopsteam flow when necessary for turbine overspeed protection.

Vitiated steam from the low-pressure turbine section 22 is directed to acondenser 30. Reactor feedwater flow from the condenser 30 includes anymakeup water flow and the flow resulting from condensation of thevitiated turbine steam as well as that resulting from condensation ofthe steam which is controllably diverted from the turbine 14 throughbypass valves 32 directly to the condenser 30. The feedwater flow isdirected from the condenser 30 to a demineralizer 34 where corrosionproducts and other impurities are removed from the fluid. From thedemineralizer 34, the feedwater is driven by one or more feedwater pumps36 through a feedwater heater system indicated in the block 26 and intothe pressure vessel of the nuclear boiling water reactor 16.

In the reactor 16, heat produced in the fuel rods contained within thefuel core is transferred to the coolant which flows along the rods.Steam is collected at the top of the pressure vessel and directedthrough one or more conduits to the turbine inlet valves 24 as indicatedby the reference character 38. Since the steam produced by the reactor16 is used directly for turbine energization, the plant operation ischaracterized as being of the single or direct cycle type.

Generally, it is necessary to hold the reactor vessel pressure within arelatively narrow range because the vessel pressure affects thereactivity rate and the reactor power operating level, i.e., the powerlevel varies directly with the reactor pressure. Accordingly, it isnecessary that the turbine throttle pressure be held within a relativelynarrow range by the imposition of throttle pressure control on theturbine inlet valve operation. Since turbine load is proportional toturbine steam flow or the ratio of impulse chamber pressure to throttlepressure (with the throttle steam at substantially constant pressure andtemperature), turbine inlet valve control cannot satisfy load demandchanges in the steady state unless changes are made in the steamgeneration rate at the steam source.

To enable turbine steam flow changes to be made to satisfy turbine andplant loading demand within the throttle pressure operating range, thereactor power operating level is changed as by changing the reactor corerecirculation flow through controlled operation of centrifugal pumps 38and 40 in recirculation flow loops 42 and 44. Jet pumps (not shown) canbe used within the reactor vessel to produce a drive flow which forcescoolant recirculation through and about the fuel core.

When it is desired to increase reactor power, steam void accumulation isreduced by increasing recirculation flow. Reduced reactor power requiresreduced recirculation flow. Typically, recirculation flow control can beused to vary reactor power over a range as high as 25 percent or more.

Larger power changes require position changes in conventional controlrods 46 to vary the amount of neutron absorption. Manual or possiblyautomatic control rod placement would normally also be subject toimplementation of a core burnup management program.

A conventional reactor control system designated by block 48 is providedfor determining the operationof the recirculation flow system and theoperation of the control rods 46. Feedback signals or data are appliedto the reactor control system 48 from predetermined reactor systemdetectors and manually or automatically operated analog controllers orother suitable control means in the reactor control system 48 generateoutputs which operate the recirculation flow pumps 38 and 40, drives 50for the control rods 46 and other reactor system control devices.

In the recirculation flow control system, conventional coolant flowdetectors (not shown) can be used to determine the flows in the loops 42and 44 for feedback comparison to an externally determined recirculationflow setpoint FSP. Similarly, suitable position detectors generatecontrol rod position feedback signals for comparison with control rodposition setpoints RSP which are determined in accordance with theexternally determined core management program and, if desired, inaccordance with any demand for reactor power change in excess of therecirculation flow control range. In this case, automatically operatedpump controllers vary the speed of the recirculation pump drives forflow correction and manually operated rod drive controllers are used tooperate the rod drives to satisfy the rod position setpoints RSP.

lnlet steam turbine valves positioning is effected by operation ofrespective conventional hydraulic inlet valve actuators 52 under thecontrol of respective electrohydraulic controls 54. A total inlet valveposition demand signal DT is applied to the controls 54 where individualinlet valve demand signals DTl,...,DTn are conventionally generated fromthe total signal DT for comparison to respective inlet valve positionfeedback signals conventionally generated by respective lineardifferential transformer or other position detectors PDlV. Positionerror for any of the inlet valves 24 results in operation of theassociated valve actuator 52 until the error is removed and the totalvalve position demand DT is satisfied.

Similarly, hydraulic bypass valve actuators 56 and electrohydraulicbypass valve controls 58 operate the bypass valves 32 to satisfy a totalbypass valve position demand signal DB for diversion of steam not neededby the turbine 14 such as during startup and shutdown and during loadcontrol when load rejection conditions are imposed on the power plant10. Bypass valve position feedback signals are generated by conventionalposition detectors PDBV for comparison to individual bypass valveposition demand signals DBl,...,DBn derived from the total bypass demandDB.

Each valve control system in the electrohydraulic controls 54 and 58includes a conventional electrical analog demand controller (notindicated) which linearly characterizes the individual valve positiondemand signal applied to its input. The demand controller output iscoupled to a conventional analog position controller (not indicated)where a valve position error signal is generated by combination of thedemand controller output and the valve position feedback signal. Theposition controller provides proportional plus reset action. lts outputoperates a servo valve which in turn operates the hydraulic valveactuator 56 until the correct valve position is obtained. For greaterdetail on the conventional aspects of electrohydraulic controls,reference is made to a paper entitled Electrohydraulic Control Forlmproved Availability and Operation of Large Steam Turbines" andpresented by M.

Birnbaum and E. G. Noyes to the ASME-IEEE National Power Conference atAlbany, New York during Sept. 19-23, 1965.

A turbine follow control system 60 is employed as shown in FIG. 2 tooperate the boiling water reactor 16 and the steam turbine 14 andprovide improved operation of the plant 10. A conventional digitalreference system 62 like that discussed in the aforementioned Bimbaumand Noyes paper is employed to generate an electrical speed referenceand an electrical load reference to which the plant operation is to beconformed as determinable respectively from the electrical outputs of aconventional speed detector 64 coupled to the turbine shaft structureand a conventional impulse pressure detector 66 coupled to the impulsechamber of the high-pressure turbine section 20.

As plant operation is being controlled to meet plant demand, throttlepressure is held below a limit value and/or within a predetermined rangeof values through the operation of a conventional analog pressurecontroller 68 or a similar backup pressure controller 70 in a throttlepressure control system 67. Throttle pressure is detected by aconventional throttle pressure detector 72 which generates an electricaloutput for summing with a suitably generated setpoint signal SP.

The pressure controller 68 or 70 can be a conventional operationalamplifier having input circuitry which performs the summing functionwith respect to the applied input signals. In this instance, thepressure controller 68 or 70 is provided with a proportionalcharacterization like that provided for pressure controllers inconventional turbine follow control systems for boiling waterreactor-steam turbine plants. However, in a manner similar to thatdescribed in the aforementioned Giras and Podolsky copendingapplication, the throttle pressure control system 67 can make use ofpressure controllers with other characterizations such as a proportionalplus reset characterization.

A suitable comparator circuit in selector block 74 operates to transferthe output of one of the pressure controllers 68 or 70 for furtherprocessing. For example, under normal conditions, the backup controller70 may be adjusted to generate a slightly larger output than thepressure controller 68 over the range of throttle pressure error inputs.The selector 74 then responds to the backup controller 70 only when itsoutput is less than that of the controller 68.

Respective analog function generator circuits 76 and 78 operate on theselected pressure controller output signal to generate the respectivevalve position demand signals DT and DB for the turbine inlet valves 24and the bypass valves 32. Preferably, the inlet valve function generator76 produces an output valve position demand signal proportional to thepressure controller output with the constant of proportionality selectedto produce a suitable closed loop gain for the inlet valve control loop.

Similarly, the bypass valve function generator 78 produces an outputvalve position demand signal proportional to the pressure controlleroutput with the constant of proportionality selected to produce asuitable closed hoop gain for the bypass valve control loop However, thetransfer function in the function generator 78 is such that no outputbegins to be generated for bypass valve control action until throttlepressure error exceeds a predetermined amount above rated throttlepressure.

The throttle pressure control system 67 accordingly maintains throttlepressure within range by turbine inlet valve control action therebydirectly affecting turbine loading or by bypass valve control actionthereby diverting unneeded steam from the turbine 14 to the condenser30. Plant load demand is met in the load control mode of operation bythe turbine 14 through follow action with reference to the boiling waterreactor 16. Thus, changes in the operating level of the reactor in theload mode of operation enable the turbine load ultimately to be adjustedto meet plant demand as throttle and reactor pressure constraints aresatisfied.

To reach the load mode of plant operation, the reactor 16 is startedwith the turbine 14 at turning gear speed, the function generator 76turned off and the reactor and throttle pressure controlled by bypassvalve operation. The function generator 78 is suitably controlled by theselector or block 74 to establish this operating mode. At an appropriatereactor operating level and at appropriate steam conditions, the turbine14 is accelerated toward synchronous speed by the use of a speed rampreference applied by the reference system 62 to a conventional speederror detector circuit 80 where it is compared with the actual speedsignal. The resultant speed error signal is characterized with percentspeed regulation as indicated by block 82 and then applied to theturbine inlet valve controls 54 where is forms the inlet valve positiondemand signal DT. The controls 54 then operate the actuators 52 tocorrect the positions of the inlet valves 24. In most instances, inletvalve sequencing is involved in inlet valve control and the controls 54accordingly include conventional sequencing control circuitry. Duringspeed control, the function generator 76 remains off and bypass systemoperation continues in order to control the throttle pressure.

After synchronization and closure of the plant breaker(s), the turbine14 is initially loaded and throttle pressure control is transferred fromthe bypass valves to the turbine valves. Such transfer is suitablyeffected, as by operation of bumpless transfer circuitry included in theselector block 74 as the function generator 76 is turned on to generatethe demand DT. After initial loading, the plant enters the load controlmode of operation in which the turbine 14 is operated under throttlepressure control to follow corrective load changes made in the reactoroperating level. In the turbine follow load control mode, the bypassvalves 32 are closed to prevent bypass steam flow except in response tooperation of the function generator 78. A computer control arrangementfor sequencing the system through the various operating modes isdescribed in the aforementioned Giras and Podolsky copendingapplication.

During initial loading and during turbine follow operation, aconventional load error detector 84 compares the load reference signalwith actual load represented by the output of the impulse pressuredetector 66 and generates an error signal which is passed through aplant safety limiter 86 and applied to the reactor control system 48. Ifdesired, the reactor load error signal can instead be developed with theuse of a megawatt transducer (not shown). At that point, the load erroris algebraically summed with any speed error or frequency participationsignal to constitute the reactor load setpoint. Reactor operation iscontrolled by the control system 48 as previously described.

As the reactor 16 is controlled to meet frequency-adjusted load demand,the pressure controller 68 or 70 generates a turbine valve controlsignal which is proportional in magnitude to the magnitude of thethrottle pressure error and which is operated upon by the functiongenerator 76 to produce the signal DT. The gain applied by the turbineinlet valve controls 54 determines the rate at which the turbine steamflow changes without exceeding throttle pressure limits until the plantload demand is satisfied.

To speed up the turbine follow control action, a conventional throttlepressure setpoint adjuster 90 is provided with a transfer functionhaving suitable dynamic characterization. lt responds to the limitedload error signal and temporarily changes the pressure controllersetpoint SP particularly when step changes are made in the load demand.

During load control, the electrical speed error signal is applied to theinlet valve controls 54 but it produces no control until turbine speedexceeds a predetermined value such as 102 percent rated. The initiationof speed control is electrically determined such as by the use of diodelogic circuitry (not shown) in the turbine inlet valve controls inputcircuitry to determine when the speed signal exceeds the assigned value.When the speed control loop becomes operative in the load control mode,the turbine valve position demand DT is made equal to the sum of thespeed control signal and the pressure control signal. The speed feedbackloop includes the speed error detector 80, the percent speed regulator82 and the electrohydraulic inlet valve controls 54. Thus, duringturbine overspeed, the speed control loop offsets pressure controloperation to produce progressive inlet valve closure as turbine speedincreases, and the initiation of the speed control is made at aparticular turbine overspeed value independent of the turbine loadlevel. Better plant operation is thus realized under turbine followcontrol and similar benefits can be realized in coordinated plantcontrol. The impulse pressure detector output is combined with theoutput of the bypass valve function generator 78 in limiter block 88 inorder to keep total reactor steam flow below a limited value.

In FIG. 3, there is shown a coordinated control system 92 arranged inaccordance with the principles of the invention to provide for improvedboiling water reactor-steam turbine plant operation. The control system92 includes components similar to those employed in the control system60 of FIG. 2 but some component differences and different interactionprovide for the improved operation.

A conventional digital reference system 94 is again employed to generatean electrical load reference and an electrical speed reference. Thespeed control channel in this case also includes a speed error detector96 which generates a speed error signal signifying the differencebetween the speed reference signal and the output signal of the speeddetector 64 which represents the actual turbine speed. The speed errorsignal is characterized with a percent regulation in block 98 andapplied to the reactor control system 48 and the electrohydraulic inletvalve controls 54 as in the case of FIG. 2. The feedback speed controlloop controls turbine acceleration during startup, frequencyparticipation during the load mode of operation, and turbinedeceleration during shutdown in those cases where turbine coastdown isnot employed.

During load control, a conventional load error detector 100 generates asignal representative of load error in response to the differencebetween the load reference signal and the output signal of the impulsepressure detector 66 which represents the actual turbine load. Afterlimiting in block 102, the load error signal is applied to the reactorcontrol system 48 to keep the reactor power level in line with plantload demand. As previously, the reactor load error signal can if desiredbe developed with the use of a megawatt transducer.

In order to produce faster, more coordinated, more efficient andeconomic and more reliable plant operation during the load control mode,the coordinated control 92 also includes a load control loop partlyindicated by the reference character 104 in which a load demand,preferably in the form of the load reference signal, is applied directlyto the electrohydraulic inlet controls 54 subject to the constraintproduced by a throttle pressure control system 106. In alternate cases,the load demand signal could be the load error signal from the detectorI00.

As changes are made in the load reference or as changes occur in theturbine load at a fixed load reference, the total inlet valve positiondemand DT is directly varied to achieve immediate inlet valve positionchange subject to the constraint imposed by the throttle pressurecontrol system 106. The valve position demand DT under normal loadoperation is generated by suitable circuitry within the block 54 as thealgebraic sum of the load reference signal, speed control signal 110 anda throttle pressure control signal 108. The throttle pressure constraintis thus imposed through variation of the total valve position demandsignal DT. The control signal 110 is continuously included in the sumDT, but, if desired, inclusion of the speed control signal 110 can beblocked (such as by diode circuitry) from the sum DT under turbineoverspeed conditions until the turbine reaches a particular overspeedvalue. Imposition of speed control then offsets load control to produceprogressive turbine inlet valve closure as turbine speed increases. Aspreviously, the initiation of speed control on overspeed then is madeindependently of the load operating level. In both FIGS. 3 and 4, thespeed regulation determines the turbine overspeed value at which fullinlet valve closure occurs.

For frequency participation required by increased loading, the speedcontrol is similarly continuously applied to the inlet valves, but itmay be applied only after a predetermined speed drop has been sensed bydiode circuitry (not shown) or other suitable means in the inputcircuitry of the inlet valve controls 54. The turbine is then preventedfrom being operated for minor frequency participation demands.

On the subject of load control again, direct load control of the inletvalve controls 54 essentially involves making use of stored energy inthe reactor steam to achieve faster load control as the reactor powerlevel is being changed to correct load demand error. In this sense, thecoordinated control system '92 is similar to the turbine follow control60 of FIG. 2 since the latter uses throttle pressure setpoint adjustmentto make use of stored steam energy for faster plant response. However,

direct load control in the coordinated control system 92 produces fasterand generally better plant performance because turbine valve movement isinitiated without the time delay of pressure control system response andfurther because the early valve movement can always be made with thebest calibration, i.e., to-the extent allowed by the throttle pressuresystem control constraint. in contrast, use of throttle pressuresetpoint adjustment in turbine follow systems involves a fixedprecharacterization of turbine valve control response withoutcalibration of all of the varying process conditions.

The total inlet valve position demand signal DT results from balancingthe load reference signal and, as applicable, the speed control signalagainst the signal 108 from the throttle pressure control system 106.The valve position feedback signals PDlV are compared to the individualvalve position demand signals DTl,...,DTn as in FIG. 2 until valveposition error is removed by proportional plus reset control action. Thepressure control signal component 108 of the valve position demandsignal DT in effect modifies the load reference signal to direct theinlet valve positioning to satisfy load demand as well as throttlepressure constraints.

In applying load demand directly to the turbine inlet valve controls 54,a positive feedback condition can tend to be created unless otherwiseprevented. For example, increased load demand requires higher steam flowand higher impulse pressure. Opening movement of the governor valves isthus required, but this causes the throttle pressure to drop which inturn causes lower impulse pressure and a need for further openingmovement of the governor valves.

The throttle pressure control system 106 allows inlet valve action to bedirected to meeting load demand within throttle pressure constraints andin doing so avoids the development of positive inlet valve feedbackaction. Thus, the pressure control signal 108 is generated by aconventional summing circuit 112 as the algebraic sum of respectivesignals from a pressure function generator 114 and a pressure errorfunction generator 116.

As in the case of FIG. 2, the throttle pressure signal is coupled fromthe throttle pressure detector 72 to the input of a pressure controller118 and a backup pressure controller 120. A setpoint SP is compared tothe signal representing actual throttle pressure and a throttle pressureerror signal is developed. in this instance, proportional action isemployed in the pressure controller 118 or 120. A selector 122 transfersthe output throttle pressure error signal from one of the pressurecontrollers 118 or 120 to the input of the function generator 116 by theselection procedure previously described. The transfer function for thegenerator 116 is like that described for the function generator 76 ofFIG. 2.

The inputs to the ratio function generator 114 are the output signalfrom the throttle pressure detector 72 and the output signal from theimpulse pressure detector 66. The output signal from the generator 114is a predetermined function of the ratio of the impulse pressure P, tothe throttle pressure P,,. Preferably, the transfer function is selectedto make the output signal from the generator 114 substantially constantwhen the turbine is held at constant load, i.e.. constant P,. Thisfeature enables throttle pressure control actions to be applied to thecontrols 54 when there is no load error. Suitable circuitry (not shown)is employed in the generator 114, for example, a conventionalpotentiometer circuit can be used to generate the ratio signal and aconventional logic-gating circuit can be used to block or pass the ratiosignal in accordance with the transfer function.

The ratio of P, to P is proportional to total inlet valve area which inturn is substantially linear with load at rated throttle pressure. Thus,the ratio of P, to P acts as a load feedback which is balanced againstthe load reference signal in forming the total demand signal DT. Theratio feedback eliminates positive feedback action since a valveposition change made to satisfy a change in P, demand causes an oppositepolarity change in the ratio. The throttle pressure control channelincluding the controller 118 or 120 and the function generator 116applies throttle pressure constraint action as load demand is satisfiedthrough the ratio feedback control.

lf desired, the summing circuit 112 can be combined in the block 54. Inthat event, the total valve position demand signal DT during loadcontrol equals the algebraic sum of the load reference signal, thepressure ratio load feedback signal, the throttle pressure constraintsignal from the function generator 116, and, as applicable, the speedcontrol signal 110.

A throttle pressure setpoint adjuster 124 is also employed in thecoordinate control system 92. The adjuster 124 responds to the limitedload error signal to lower or raise the pressure controller setpoint SPwithin limits to prevent closing or opening of the turbine inlet valvesrespectively on increases or decreases in load demand. If throttlepressure falls below or rises above the adjusted setpoint, the controlsystem causes the turbine inlet valves to close or open as the case maybe.

The pressure control system 106 also includes a bypass valve functiongenerator 126 which provides a bypass valve control signal in the mannerdescribed for FIG. 2 so that steam not needed by the turbine 14 duringload control is diverted directly to the condenser 30. The total bypassvalve demand signal DB is derived from the bypass control signal subjectto and impulse pressure limited by a limiter 128.

Improved boiling water reactor-steam turbine plant operation resultsfrom use of the invention. The improvement includes better performancewith greater economy, efficiency and reliability. The coordinatedcontrol provides faster and more coordinated plant operation withinplant performance capabilities. The improved coordination includesimprovement in the relative operating dynamics of the boiling waterreactor and the steam turbine as well as other improvements such as aninherent capability for immediate load control of the turbine valves inthe event of loss of pressure control.

Electrohydraulic controls are used in both the turbine follow andcoordinated control modes of plant operation. The electrical parts ofthe systems are herein described in analog terms, but digital systemsincluding digital computers can be employed to effect the disclosedsystem functioning. Further, either analog or digital control systemscan employ hardware and/or software control circuitry which differs indetail from that described herein particularly insofar as thecoordinated control system is concerned. For example, computer controlcan be used to effect turbine valve positioning in a manner like thatdescribed in a paper entitled Digital Control For Large SteamTurbine-Generators" and presented by T. C. Giras and M. Bimbaum to theAmerican Power Conference in Chicago, Illinois on Apr. 23-25, I968.Feedforward and computer control can be employed for boiling waterreactor-steam turbine plant operation in the manner disclosed in theaforementioned Giras and Podolsky application. In digital computercontrol, many control functions embraced by the invention are performedby software control circuitry (i.e., software execution) as opposed toanalog control circuitry (i.e., hardware operation The foregoingdescription has been presented only to illustrate the principles of theinvention. Accordingly, it is desired that the invention not be limitedby the embodiment described but rather that it be accorded aninterpretation consistent with the scope and spirit of its broadprinciples.

What is claimed is:

1. A system for controlling the operation of a nuclear boiling waterreactor-steam turbine plant, said system comprising means for generatingan electrical representation of a load demand reference and anelectrical representation of a turbine speed demand reference, means forgenerating an electrical representation of actual turbine speed, meansresponsive to the load reference representation for controlling theoperation of the reactor to meet load demand, means for generating anelectrical representation of the throttle pressure of steam supplied tothe turbine by the reactor, an electrohydraulic control system foroperating steam inlet valves associated with the turbine, anelectrohydraulic control system for operating steam bypass valves todivert steam from the turbine to a condenser under predeterminedthrottle pressure conditions, means responsive to the throttle pressureelectrical representation for operating said inlet valve control systemto constrain the throttle pressure within predetermined limits, meansfor generating an electrical representation of turbine speed error fromthe speed reference and actual speed representations, and means foroperating said inlet valve control system in response to the speed errorrepresentation at a predetermined turbine overspeed independent ofturbine load.

2. A plant control system as set forth in claim 1 wherein said systemoperates in the turbine follow mode and a throttle pressure controlsystem includes the first-mentioned inlet valve control system operatingmeans and primarily determines the operation of said inlet valve controlsystem.

3. A plant control system as set forth in claim 2 wherein saidelectrohydraulic control systems include electrical control circuitryformed principally from analog circuits.

4. A plant control system as set forth in claim 1 wherein said systemoperates in a coordination control mode, and a throttle pressure controlsystem includes the first-mentioned inlet valve control system operatingmeans to produce throttle pressure constraint on the operation of saidinlet valve control system, and means responsive to the load referencerepresentation is provided for directly controlling the operation ofsaid inlet valve control system to produce load corrective positioningof the turbine inlet valves within throttle pressure constraints.

5. A system for controlling the operation of a nuclear boiling waterreactor-steam turbine plant, said system comprising means for generatingan electrical representation of a load demand reference, meansresponsive to the load reference representation for controlling theoperation of the reactor to meet load demand, an electrohydrauliccontrol system for operating steam inlet valves associated with theturbine, an electrohydraulic control system for operating steam bypassvalves to divert steam from the turbine to a condenser underpredetermined throttle pressure conditions, means for generating anelectrical representation of the throttle pressure of steam supplied tothe turbine by the reactor, and means responsive to the load referenceand throttle pressure electrical representations for controlling theoperation of said inlet valve control system to adjust the turbine loadtoward plant demand within throttle pressure constraints and withoutpositive feedback effect on impulse pressure as the reactor power levelundergoes correction.

6. A plant control system as set forth in claim 5 wherein means areprovided for generating an electrical representation of the ratio of theturbine, impulse pressure to the throttle pressure, said controllingmeans for said inlet valve control system provides inlet valve operatingcontrol at least in response to the pressure ratio and load referenceand throttle pressure electrical representations, and said controllingmeans for said inlet valve control system includes said ratio generatingmeans.

7. A plant control system as set forth in claim 6 wherein means areprovided for generating a representation of throttle pressure error inresponse to the throttle pressure electrical representation, and saidcontrolling means for said inlet valve control system includes saidthrottle pressure error generating means.

8. A plant control system as set forth in claim 6 wherein said ratiogenerating means generates an electrical representation as apredetermined function of the ratio of the turbine impulse pressure tothe throttle pressure, and the pressure ratio representation issubstantially constant for constant turbine impulse pressure.

9. A plant control system as set forth in claim 8 wherein saidcontrolling means for said inlet valve control system includes at leastone analog pressure controller responsive to a throttle pressuresetpoint and an actual throttle pressure signal to generate a throttlepressure error signal, said electrohydraulic inlet valve control systemincludes electrical circuitry formed principally from analog circuits,and means responsive at least to the throttle pressure error signal andthe load demand electrical reference representation and the pressureratio representation are provided to generate a valve position demandsignal for said electrohydraulic inlet valve control system.

10. A plant control system as set forth in claim wherein saidreactor-controlling means includes means responsive to the loadreference representation and an electrical representation of actual loadto generate a load error representation upon which reactor controlactions are based.

11. A method for controlling the operation of a nuclear boiling waterreactor-steam turbine plant, the steps of said method comprisinggenerating an electrical representation of a load demand reference,controlling the operation of the reactor to meet the load demand inaccordance with the load reference representation, generating anelectrical representation of the throttle pressure of steam supplied tothe turbine by the reactor, controlling the operation of turbine steaminlet valves by means of an electrohydraulic control system, controllingthe operation of steam bypass valves to divert steam from the turbine toa condenser under predetermined throttle pressure conditions by means ofan electrohydraulic control system, and controlling the operation of theinlet valve electrohydraulic control system in response to the loadreference representation and the throttle pressure electricalrepresentation to adjust the turbine load toward plant demand withinthrottle pressure constraints and without positive feedback effect onimpulse pressure as the reactor power level undergoes correction.

i i t i i

2. A plant control system as set forth in claim 1 wherein said systemoperates in the turbine follow mode and a throttle pressure controlsystem includes the first-mentioned inlet valve control system operatingmeans and primarily determines the operation of said inlet valve controlsystem.
 3. A plant control system as set forth in claim 2 wherein saidelectrohydraulic control systems include electrical control circuitryformed principally from analog circuits.
 4. A plant control system asset forth in claim 1 wherein said system operates in a coordinationcontrol mode, and a throttle pressure control system includes thefirst-mentioned inlet valve control system operating means to producethrottle pressure constraint on the operation of said inlet valvecontrol system, and means responsive to the load referencerepresentation is provided for directly controlling the operation ofsaid inlet valve control system to produce load corrective positioningof the turbine inlet valves within throttle pressure constraints.
 5. Asystem for controlling the operation of a nuclear boiling waterreactor-steam turbine plant, said system comprising means for generatingan electrical representation of a load demand reference, meansresponsive to the load reference representation for controlling theoperation of the reactor to meet load demand, an electrohydrauliccontrol system for operating steam inlet valves associated with theturbine, an electrohydraulic control system for operating steam bypassvalves to divert steam from the turbine to a condenser underpredetermined throttle pressure conditions, means for generating anelectrical representation of the throttle pressure of steam supplied tothe turbine by the reactor, and means responsive to the load referenceand throttle pressure electrical representations for controlling theoperation of said inlet valve control system to adjust the turbine loadtoward plant demand within throttle pressure constraints and withoutpositive feedback effect on impulse pressure as the reactor power levelundergoes correction.
 6. A plant control system as set forth in claim 5wherein means are provided for generating an electrical representationof the ratio of the turbine impulse pressure to the throttle pressure,said controlling means for said inlet valve control system providesinlet valve operating control at least in response to the pressure ratioand load reference and throttle pressure electrical representations, andsaid controlling means for said inlet valve control system includes saidratio generating means.
 7. A plant control system as set forth in claim6 wherein means are provided for generating a representation of throttlepressure error in response to the throttle pressure electricalrepResentation, and said controlling means for said inlet valve controlsystem includes said throttle pressure error generating means.
 8. Aplant control system as set forth in claim 6 wherein said ratiogenerating means generates an electrical representation as apredetermined function of the ratio of the turbine impulse pressure tothe throttle pressure, and the pressure ratio representation issubstantially constant for constant turbine impulse pressure.
 9. A plantcontrol system as set forth in claim 8 wherein said controlling meansfor said inlet valve control system includes at least one analogpressure controller responsive to a throttle pressure setpoint and anactual throttle pressure signal to generate a throttle pressure errorsignal, said electrohydraulic inlet valve control system includeselectrical circuitry formed principally from analog circuits, and meansresponsive at least to the throttle pressure error signal and the loaddemand electrical reference representation and the pressure ratiorepresentation are provided to generate a valve position demand signalfor said electrohydraulic inlet valve control system.
 10. A plantcontrol system as set forth in claim 5 wherein said reactor-controllingmeans includes means responsive to the load reference representation andan electrical representation of actual load to generate a load errorrepresentation upon which reactor control actions are based.
 11. Amethod for controlling the operation of a nuclear boiling waterreactor-steam turbine plant, the steps of said method comprisinggenerating an electrical representation of a load demand reference,controlling the operation of the reactor to meet the load demand inaccordance with the load reference representation, generating anelectrical representation of the throttle pressure of steam supplied tothe turbine by the reactor, controlling the operation of turbine steaminlet valves by means of an electrohydraulic control system, controllingthe operation of steam bypass valves to divert steam from the turbine toa condenser under predetermined throttle pressure conditions by means ofan electrohydraulic control system, and controlling the operation of theinlet valve electrohydraulic control system in response to the loadreference representation and the throttle pressure electricalrepresentation to adjust the turbine load toward plant demand withinthrottle pressure constraints and without positive feedback effect onimpulse pressure as the reactor power level undergoes correction.